Influence of inclined plates on flow characteristics of a liquid-solid fluidised bed: A CFD-DEM study

Abstract

An in-depth analysis of liquid-solid flow characteristics of a modified fluidised bed equipped with inclined channels has been conducted using a coupled model of computational fluid dynamics (CFD)-discrete element method (DEM). Specifically, the simulation results have provided local information on the two phase flow characteristics of the modified fluidised bed including solid distribution, particle velocity distribution and energy dissipation rate of the liquid flow. It is shown that the strong reflux of sediments from the inclined channel into the bottom vertical section induced intensive circulations of both solid particles and the liquid phase. As a result, solid distribution over the entire bed became more non-uniform as the fluidisation velocity increased. Moreover, the subsequent impingement of the liquid-solid flow onto channel walls resulted in a much higher energy dissipation rate of the liquid flow, indicating a higher energy loss when compared to conventional fluidised beds. Also, an optimum fluidisation velocity was identified at which the solid concentration of the sediment layer reached its peak. It was shown that smaller inclination angle led to lower bed expansions and greater solid reflux, resulting in stronger two-phase flow circulations in the vertical section. For fluidised beds with multiple inclined channels, the particle flow characteristics in individual inclined channels were observed to be rather similar with smaller overall particle velocities and more compact sediments. The predicted results of the CFD-DEM model were found to be in good agreement with the experimental data and those predicted by our kinematic model, with a maximum deviation of 12%. The CFD-DEM model presented here can be utilised to optimise the design and operation of liquid fluidised beds containing inclined channels.